The complexion of the Boston Celtics' opening-round series against the Chicago Bulls changed dramatically when Doc Rivers told reporters Thursday that Kevin Garnett will not be ready to start the series and is unlikely to return to the lineup anytime soon.

You've probably seen that Boston won at a .772 clip this season with Garnett in the lineup, as compared to a .720 pace in the 25 games he missed. That difference understates the magnitude of Garnett's value to the Celtics. In games Garnett played, Boston outscored opponents by 9.2 points a night--a mark that ranked second in the league behind the Cleveland Cavaliers. Without him, that sank all the way to a plus-3.8 differential, well below that of the league's top teams, as well as the Portland Trail Blazers and Houston Rockets.

As you dig deeper into the numbers, the difference is obvious: Defense. As John Hollinger has pointed out, the Celtics truly missed last season's Defensive Player of the Year and the anchor of the league's best defense in 2007-08. Boston still finished the season with the league's second best Defensive Rating, trailing only the Orlando Magic, but the Celtics saw their points allowed per 100 possessions shoot up from 100.8 with Garnett--far better than the Magic's 103.0 Defensive Rating--to a whopping 109.6 when Garnett sat out.

Breaking defense down into Dean Oliver's Four Factors shows that the Celtics missed Garnett's defense in virtually every area. Opponents shot better on both twos and threes, grabbed far more offensive rebounds, and turned the ball over less frequently. Surprisingly, the biggest difference at the defensive end was in forcing turnovers--not exactly Garnett's specialty. His defensive presence still made the difference between Boston's being one of the league's five best defenses at forcing turnovers (14.8 percent of possessions with him) and one of its five worst (12.1 percent of possessions without him).

At the other end of the floor, Boston has actually thrived without Garnett. The Celtics' drop-off on defense is somewhat offset by the fact that they have pushed their Offensive Rating from 111.4 points per 100 possessions to 115.2 in Garnett's absence.

With the "Big Three" reduced to a pair of players, Paul Pierce has taken a much more active role in Boston's offense. He's used on 27.9 percent of the team's possessions, compared to 24.3 percent when Garnett plays. Despite the heavier load, Pierce has been a more efficient scorer, allowing him to push his scoring average to 24.1 ppg from the 18.9 he was averaging alongside Garnett.

Point guard Rajon Rondo has also taken advantage of Garnett's absence to look more for his own scoring, instead of just setting up his teammates. Rondo's usage rate is up slightly, while his True Shooting Percentage has gone from 53.0 percent to 57.3 percent. So while he averaged nearly an assist more per game when he had Garnett on the receiving end, that has been offset by Rondo's scoring increase from 11.2 ppg to 13.6.

The offense got a further boost late in the regular season when backup forward Leon Powe returned from a knee injury of his own, which cost him 12 games. While Doc Rivers favored Glen Davis over Powe when both were healthy and Garnett was out, Powe is the more efficient scoring threat in the paint and offers punch off the bench that was lacking in his absence.

The new perimeter-oriented Boston attack could cause problems for a Chicago team that has badly slipped defensively in its first year under Vinny Del Negro. Once defensive stalwarts, the Bulls ranked 18th in the league in Defensive Rating this season. Chicago was especially vulnerable on the defensive glass, ranking 28th in the NBA in defensive rebounding. Meanwhile, the Celtics' post-Garnett offensive boardwork was among the five best in the league, with Davis and Kendrick Perkins combining for more than five offensive rebounds a night in that stretch.

In Kirk Hinrich, the Bulls have a quality defender at guard who has bothered Ray Allen in the past. Putting Hinrich on the floor, however, means sacrificing either Ben Gordon's potent scoring ability or the steady hand of rookie Derrick Rose at the point. The quick Rondo especially could pose problems for Chicago's backcourt, which has been less effective defensively against point guards this season. In Tyrus Thomas, the Bulls have a good shot-blocker to provide help, but they have been vulnerable to putbacks and other scores in the post when Thomas has had to leave his own man.

Having improved since dealing for John Salmons and Brad Miller at the trade deadline, the Bulls have a deep enough rotation to test a Garnett-less Celtics squad. Even without Garnett, however, Boston has the better offense and the better defense. That and home-court advantage should be more than enough to keep the Celtics alive long enough to hope Garnett can rejoin them when their task gets much more difficult--because the Magic and Cavs should be waiting down the line.

Kevin Pelton is an author of Basketball Prospectus.
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